Field of Invention
The present invention relates to a high-speed steel, and more particularly to a spray-formed high-speed steel.
Description of Related Arts
Because of the slow cooling velocity during the casting process, the high-speed steel prepared through the conventional method has a serious segregation of the alloying elements, forming coarse crystalline grains and carbides. Even after the subsequent thermal deformation process, the nonuniformity of the structure is difficult to be completely eliminated, thereby causing the performance of the high-speed steel at a relatively low level.
In order to restrain the segregation of the alloying elements during processing, for obtaining the alloy having the uniform structure, a technology, which prepares the high-speed steel and the tool and die steel through the powder metallurgy process, is developed. Although the powder metallurgy process has a relatively mature development, by which the high-quality high-speed steel is manufactured, the powder metallurgy process has the long process flow and the high manufacture cost and energy consumption, causing a high price of the product.
How to improve the product quality with the relatively low process cost is a technical problem required to be solved in the conventional high-speed steel preparation. The spray forming process provides a way to solve the above problem. Spray forming is a short flow process, for rapidly cooling and shaping the liquid steel, which is able to solve the segregation problem of the alloying elements during the conventional casting preparation process and the cost increase problem caused by the long process flow of the powder metallurgy process. The high-speed steel prepared through the spray forming process has the following problems. With spray forming, the size of the cross section of the ingot increases; during spray deposition, the solidification velocity of the liquid steel at the end of the ingot relatively decreases; and, for the high-speed steel having the characteristics of high melting temperature, wide solidification temperature range, and multiple phase compositions, the segregation of the alloying elements easily occurs at the local ingot, forming the coarse structure, which further affects the product quality.